Regarding your first question, it is not possible to give an exact linear conversion factor for the Blue to UV reading because it changes with increasing highlight density, and it also varies with films. However, in general it would be pretty safe to say that a blue channel reading of log 1.3 will read a bit more than log 1.7-1.8 in UV mode. However, a blue channel reading of 1.0 would read only about 1.25 in UV.
About the issue of AZO sensitivity, it is true that this paper has its maximum sensitivity in the UVA range, and drops off rapidly in the near visible range. However, because of the speed of the paper most people do not use UV light to expose. The use of a UV lights of the type we use in alternative photograhy would result in impossibly short exposures. So in practice most people are exposing with lights that emit very little if any UV radiation and it is only the light in the blue range over about 420 nm that is effectively available to the process .
That is at least what I believe to be the case based on my conversations with a number of AZO printers.